The present invention relates to an expendable gas turbine engine, and more particularly to a start system utilizing a relatively large high pressure oxygen source.
Miniature turbojet engines are often utilized in single usage applications such as reconnaissance drones, cruise missiles, decoy and other weapon applications including air-launched and ground-launched weapon systems. The use of such an engine greatly extends the range of the weapon in comparison to the more conventional solid fuel rocket engine. Miniature gas turbine engines are difficult to fabricate sufficiently economically for general expendable usage in large numbers.
To achieve economically feasible extended range expendable propulsion sources for such weapon systems, it is necessary that not only the gas turbine engines themselves be manufactured relatively inexpensively, but that their peripheral systems must likewise be manufactured relatively inexpensively. Notwithstanding the concern for inexpensive systems, a high degree of reliability is still paramount.
Peripheral systems employed for starting an expendable gas turbine engine are of particular concern as the failure to reliably start the gas turbine engine results in a failure of entire weapons system. Moreover, many weapon systems with gas turbine engines are commonly air launched from an airborne launch platform at a relatively high altitude. High altitude starting of a miniature gas turbine engine may be particularly difficult to achieve due to difficulties with combustor light-off.
Traditional start systems for expendable gas turbine engines consist of pyrotechnic gas generators and pyroflare igniters. At high altitudes, oxygen injection is often provided to enhance combustor light-off reliability and combustor stability during the rapid engine acceleration produced by the pyrotechnic gas generator. In a start sequence for a traditional gas turbine engine, the pyrotechnic gas generator is ignited to spin up the engine by impinging upon the turbine or compressor. The pyroflare igniter provides a source for fuel light-off within the combustor. Although highly effective and reliable, traditional start systems are a relatively expensive peripheral system utilized in an expendable role.
Accordingly, it is desirable to provide a highly reliable, inexpensive starting system for an expendable gas turbine engine.